Student participation in the science practices is more than following directions to conduct pre-determined experiments and analyze data with expected solutions. This requires classroom shifts that increase the epistemic agency of students: increase student involvement and authority in developing science knowledge and practices, rather than the teacher and textbook serving as sole sources of authority. In previous work, the authors described how three teachers differentially create opportunities for students to act as epistemic agents and to engage in collective knowledge-building work. The descriptive nature of this previous research provided information about what variability can look like in classrooms attempting these reform-oriented pedagogical shifts. This paper extends this prior work by presenting an expanded, but still exploratory analysis of how those three teachers, who participated in the same professional development community and were working with common instructional materials, attempted to support student agency through science practices in a common lesson. The present goal is to use a multi-case study to identify emerging variations in key elements of knowledge and practice for inviting students' epistemic agency, even as teachers work toward specific learning goals. From these cases the research is advanced by building theoretical conjectures that can be explored further in future work about how teachers' choices about collective knowledge building may yield differential opportunities for students to experience epistemic agency.